Tourism leaders from around the world were stranded on London's buses and trains in a series of embarrassments for those promoting the 2012 Olympics.

The transport failures raised fresh doubt over the capital's ability to cope with a deluge of visitors for important events.

Barbara Follett, the Tourism Minister, apologised yesterday after Underground problems and heavy congestion caused delays for 50,000 people attending the world's largest tourism trade show at an Olympics venue in East London.

The debacle came as senior executives at Live Nation, the country's biggest events promoter, told The Times that London's reputation was being tarnished on an international scale because its transport system was “simply not good enough”.

Industry sources said that it was becoming increasingly difficult to travel to sporting, music and cultural events because of Tube closures, a strained network and congestion on the roads.

On Monday the opening of the World Travel Market at the ExCeL Centre in Docklands had to be delayed when thousands of delegates were left stranded on their way to the event.

Ertugrul Gunay, Turkey's Culture and Tourism Minister, was 25 minutes late for his press conference after a train broke down on the Docklands Light Railway and passengers were ushered on to replacement buses that then became stuck in traffic. “It is obvious traffic will pose a problem [in 2012],” he said. “I thought Istanbul was bad enough.”

Underground problems caused further delays yesterday as tourism leaders from countries including Peru, Switzerland, Egypt and Kenya attended a summit led by Ms Follett at the venue, which will host ten Olympic and Paralympic sports during the Games.

Ms Follett told them: “I apologise on behalf of the Government for the difficult journey that you have had for the two days reaching here. The weather and transport system can be variable in this country.”

John Probyn, the festival director at Live Nation, told The Times that London's transport system had an awful international reputation and “it is getting worse”. He said that while Madonna had arrived late on stage for her concert in September, it was “just crazy” that there was no room for error when 80,000 people were attending an event. “For a major city, it's so frustrating in London sometimes,” he said. “London Underground do try really hard but they are not allowed to get creative with their scheduling [for improvement works]. It's not good enough. You go to New York or Singapore and you can go anywhere you want, any time of the day.”

Transport for London (TfL) is overseeing a series of improvements, planned over several years, which result in regular closures on main routes such as the Piccadilly Line. It says that it tries to avoid closures during large events, but that they are sometimes unavoidable.

Business leaders said that problems were unfortunate but inevitable as the transport network desperately needed upgrading.

A TfL spokesman apologised for the disruption and said: “We acted swiftly to resolve the issues.”